The present invention relates to heating systems and, in particular, to timers for disabling that portion of a furnace which fires it for the purpose of providing potable hot water.
A known furnace employs an aquastat to keep the internal furnace temperature above a preset minimum. This aquastat, a thermostatic device, assures that the furnace is sufficiently warm to heat potable water through an associated heat exchanger. This known furnace also employs a room thermostat to fire the furnace and provide space heating. A disadvantage with this kind of furnace control is that the furnace cycles regularly solely to keep its internal temperature sufficiently high to operate the heat exchanger even when there is no demand by an occupant for potable hot water. For example, the aquastat subsystem may periodically fire the furnace during sleeping hours or other intervals when there is no need for domestic hot water.
A known furnace control reduces the internal furnace temperature when the outside temperature is high. This feature can be disabled by a timer when hot water is needed. However, this system will always cycle the furnace to maintain some elevated internal temperature. Also, these systems for modulating boiler temperature are relatively complex, requiring significant modification of the existing furnace controls.
It is known to provide a timed thermostat to reduce the demand for heat from a furnace and simultaneously disable a separate hot water heater during prescheduled time internals. However, this type of system does not teach how to control a dual function furnace employing an internal aquastat subsystem. The appropriate technique for disabling the foregoing furnace aquastat without eliminating the space heating provided by the furnace has not been developed.
Thus there is a need for simple equipment to reduce fuel consumption in a furnace and still obtain from it domestic hot water.